Method for wireless communication transfer with an implanted medical device

ABSTRACT

Disclosed herein is a method and apparatus for wireless communication with a medical device implanted in the human body. In the method disclosed herein an information input signal undergoes an angle modulation in a transmitter and reaches a receiver through a transmission channel. Angle modulated information carrying pulses with a frequency spectrum are generated. The pulses are time compressed in the receiver using a filter with frequency dependent transit time. The pulses are created with shortened duration and increased amplitude compared to emitted pulses. The pulses on the transmitter side are imprinted with at least part of information constituting a message using a further modulation or encoding procedure of telecommunications. At least part of the information constituting the message is additionally imprinted onto the angle modulation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

An early method for working with a high frequency carrier signal isdisclosed in the German patent application DE 196 01 866.

Various methods and devices are known to transmit signals between amedical device, in particular an implanted one, and an externaltransmitter or receiver. For example, modern cardiac pacemakers canrecord an intracardial electrocardiogram (IECG) using the pacemakerelectrodes and can transmit it, using a telemetry unit, to anextracorporeal control device.

2. Description of Related Art

In modern signal transfer methods that are known for implanted cardiacpacemakers, e.g. from the book by John G. Webster (Editor): “Design ofCardiac Pacemakers”, section 12 “External Programming”, IEEE Press BookSeries, New York 1995, the digital signal that is to be transferredwirelessly is modulated onto the high frequency carrier signal in bitsequences by a modulator in the transmitter. It is then transmittedacross a distance to the receiver, which contains a correspondingdemodulator for recovery of the data signal. The carrier signal is in acomparatively low frequency range, since it has to penetrate the bodyand must not interfere with neighbouring medical devices.

All such methods have the disadvantage that the quality of the datasignal that is recovered on the receiver side strongly deteriorates withthe distance between transmitter and receiver, and with interference inthe transmission path.

The transmitting power must not fall below a definite value, so that adesired range with a prescribed certain noise immunity can be achievedin an information transfer over a noisy transmission path.

This required high transmitting power, on one hand, has the disadvantagethat the energy consumption during the transmitting operation iscorrespondingly high, which is of disadvantage for battery operateddevices, such as the previously mentioned cardiac pacemakers, due torapid battery exhaustion. On the other hand, one is concerned that theelectromagnetic radiation emitted from the transmitter can lead to harmto the human body, which must in particular be considered for implantedmedical devices due to the extremely low distance from the patient.

SUMMARY OF THE INVENTION

The objective of this invention is to create a method of the previouslymentioned type and an arrangement for the implementation of that method,which allows a lowering of the transmitting power and an increase inrange for medical implants—while at least maintaining the transmissionquality.

The invention incorporates the technical principle, to subject thepulses, modulated with the information, using a known method oftelecommunications, to an angle modulation in the transmitter. (Anglemodulation is to be read as a generic term for phase and frequencymodulation) These angle modulated pulses are time compressed in thereceiver by introducing a time delay using suitable means, so that theduration of the pulses is shortened and they experience an amplitudeenhancement. This pulse compression can be carried out using adispersion filter. The information can be recovered from the pulsesprocessed in this manner by a corresponding demodulation, whereby thedemodulation can be carried out with an improved signal/noise ratio, dueto the increase in amplitude. The actual information can be imprintedonto the pulse by a pulse modulation method, or by carrying out thepulse compression in a discernibly different manner for pulsessequential in time, so that the information is contained in thisvariation of the angle modulation.

Thus a signal is available after the demodulation, that otherwise couldonly be obtained by using higher transmitting power, if not using anyother costly methods to improve reception, such as diversity receptionor signal encoding, which occupies a larger frequency range or a longertransmission time due to redundant components, so that the availabledata channel would show a lower data throughput or could only be used bya lower number of users.

In this invention, the angle modulation of the pulses in the transmitteris carried out according to a modulation that, during the pulseduration, determines a change in frequency, in case of a frequencymodulation, or a shift in phase, in case of a phase modulation. Phaseand frequency modulation are both treated under the common generic termof angle modulation.

While the modulation of the pulses can be achieved using different pulsemodulation methods, in the variable angle modulation a special anglemodulation time characteristic is used, corresponding to a “modulationcharacteristic curve”.

Hereby, the modulation characteristic curve—here referred to asmodulation characteristic—determines the time behaviour of the frequencyduring the pulse duration. Preferably, the frequency of the transferredsignal decreases linearly during the pulse duration, from a value abovethe carrier frequency to a value below the carrier frequency. The filteron the receiver side is matched to the employed modulationcharacteristic by a corresponding differential, frequency dependentdelay time response, in such a manner so that the generated signalcomponents of different phase position superpose to form a nearlycoincident signal.

The imprinting of the information to be transmitted can occur either byvarying or selecting the modulation characteristic, or by any otherconventional modulation method that has no effect on the signal delaytime, or only to a secondary degree. A preferred option is themodification of the amplitude of the transmitted signal dependent on theinput signal—i.e. amplitude modulation, or all types of encoding inwhich the transmitted information is determined by the type, number,position, or sequence of the transferred pulses.

The invention offers in an advantageous manner the possibility totransmit signals to devices, in particular implanted ones, using higherfrequencies than customary until now, without affecting the tissue onone hand, and without electromagnetic interference (EMI) to otherdevices used in the clinical environment on the other hand. Until nowthis was the main problem in the use of devices emitting electromagneticwaves in clinical surroundings. Until now these conditions ruled out,for example, the use of portable telephones etc. Additionally, thisinvention's method offers the advantage that a signal transfer can bemade across larger distances (for example within a patient's room), sothat programming devices etc. do not have to be attached directly to thepatient's body. When appropriate codes are selected, it is also possibleto communicate in parallel with several devices without mutualinterference. Since the used signals can be transmitted with lowamplitude, they do not rise above the surrounding noise level, or onlynegligibly. Thus the mutual interaction between them is low.

In a preferred embodiment of the invention the imprinting of theinformation of the input signal occurs by selecting or modifying amodulation characteristic dependent on the input signal. If the inputsignal has a high-level, then, for example, a modulation characteristiclinearly falling with the signal is used, which leads to a frequencymodulated pulse in which the frequency decreases during the pulseduration. For a low-level of the input signal a linearly risingmodulation characteristic is used, which correspondingly leads to apulse with frequency that increases during the pulse duration. Thefilter means on the receiver side are appropriately matched.

The invention is not limited to linear modulation characteristics, butcan be implemented with modulation characteristics of any shape, wherebyit is only necessary to assign distinct modulations to different levelsof the input signals, so that a subsequent signal discrimination ispossible in the receiver.

It is also possible to use more than two modulation characteristics forthe input signal, so that every pulse transmits a larger informationcontent. If, for example, four different modulation characteristics areavailable, then correspondingly four different pulses can betransmitted, which corresponds to a data content of 2 bits for each ofthe transmitted pulses. By increasing the number of distinct modulationcharacteristics the data transfer rate can be increased advantageously,whereby it must be noted that it becomes more difficult to distinguishbetween the frequency modulated pulses when a very large number ofmodulation characteristics are used, which increases the transfer'ssusceptibility to errors.

In the previously described embodiment of the invention the modulationof pulses occurs actively for both a high-level as well as for alow-level of the digital input signal. This means that during alow-level and a high-level of the input signal, frequency modulatedpulses are generated, that are distinguished by the frequency changeduring the pulse duration. Thus hereby, the imprinting of theinformation contained in the input signal onto the transferred signal isachieved through selection or variation of the modulation characteristicdepending on the input signal.

In another variation of the invention, the angle modulation of thepulses in the transmitter occurs independently of the input signal to betransmitted, according to a single default modulation characteristic,which determines the variation of frequency or phase during the durationof a pulse. The imprinting of the information contained in the inputsignal onto the transmitting signal can be effected in various ways,according to well known digital modulation methods. It is favourable tocarry out a pulse position modulation (PPM), in which the position ofthe individual frequency modulated pulses is modified depending on theinput signal.

In a preferred embodiment of the invention, the imprinting of theinformation contained in the input signal onto the transmitting signalis effected by pulse code modulation (PCM), in which the sequence of thepulses to be transferred is modified depending on the input signal. Fora digital input signal the transfer of the input signal occurs activelyonly for one level, whereas no pulse is generated for the other level,so that the different pulses are only distinguished by their amplitude.For a high level of the input signal preferably a linearly risingfrequency modulated pulse is generated, while for a low level a pausewith the length of the pulse is inserted. This variation of theinvention allows implementing a modulation of the pulses of the digitalinput signal with only one modulation characteristic.

In this present design for imprinting the information contained in theinput signal onto the transmitting signal, the invention is not limitedto the previously mentioned pulse position modulation or pulse codemodulation, but can in principle be implemented with all known digitalmodulation methods.

The transmitter transfers the signal, frequency modulated by one of thepreviously described methods, across the transmission path to areceiver, where it is demodulated to recover the data signal.

Here, and in the following, the term transmission path should be takengenerally, as comprising all wireless transmission paths in which thedata transfer from the transmitter to the receiver occurs by means ofelectromagnetic waves.

To be able to distinguish the frequency modulated pulses, generated bythe transmitter, from noise signals in the receiver, these pulses arecompressed in the receiver, which leads to a corresponding increase inamplitude by increasing the signal/noise ratio.

A further advantage of this invention's method is a significantly lowerinterference potential compared to other transmitters and receivers,because a predetermined signal to noise ratio can be achieved with alower transmitting power after the pulse compression in the receiver. Inaddition, the lower demands on the transmitting power lead to a loweredenvironmental impact by electromagnetic radiation.

To compress the pulses picked up on the receiver side, which arefrequency modulated according to the modulation characteristic used bythe transmitter, the received signal is filtered by a dispersion filterwith a predetermined, frequency dependent, differential delay timeresponse.

In the invention's variation that uses only a single modulationcharacteristic for generating a frequency modulated pulse on thetransmitter side, described above, only a single dispersion filter isrequired on the receiver side, whereby the frequency dependent delaytime response of this dispersion filter is matched to the modulationcharacteristic of the angle modulation carried out on the transmitterside in such a way, that the spectral signal components of the frequencymodulated pulse generated on the transmitter side arrive essentiallycoincident at the output of the dispersion filter, which leads to apulse compression and a corresponding increase in amplitude. If theangle modulation on the transmitter side is effected according to alinearly falling modulation characteristic, then the frequency of thepulse decreases during the pulse duration, which results in an arrivalat the receiver of the high frequency signal components side before thelow frequency signal components. The delay time response of thedispersion filter on the receiver side must compensate for this “lead”of the high frequency signal components, so that the spectral signalcomponents of the frequency modulated pulse superpose to form a pulsewith increased amplitude at the output of the dispersion filter.

The recovery of the information contained in the input signal is carriedout by a detector connected after the dispersion filter, which ismatched to the modulation method, that is used on the transmitter sidefor imprinting the information contained in the input signal.

If, depending on the amplitude of the input signal, one of severalmodulation characteristics is selected on the transmitter side,preferably a linearly falling modulation characteristic for ahigh-level, and a linearly rising modulation characteristic for alow-level of the input signal, then fundamentally two options exist forthe interpretation in the receiver.

One option is to provide only one dispersion filter on the receiverside, the delay time response of which is matched to the modulationcharacteristic used on the transmitter side, in a manner so that thespectral signal components of the pulse, frequency modulated accordingto this modulation characteristic, arrive essentially coincident at theoutput of the dispersion filter, which leads to a pulse compression andincrease in amplitude. If the frequency modulation on the transmitterside occurs according to one of the other modulation characteristicsthat are not optimally matched to the delay time response of thedispersion filter on the receiver side, then the spectral signalcomponents of the frequency modulated pulse arrive at the output of thedispersion filter distributed over time, and thus, due to the lowerpulse compression or expansion, also with a smaller amplitude. In thisembodiment, the amplitude of the pulse that arrives at the output of thedispersion filter depends on the modulation characteristic used at thetransmitter side, and thus on the amplitude of the input signal employedin the selection of the modulation characteristic. A detector that canbe executed, for example, as an amplitude demodulator, is connectedafter the dispersion filter, to recover the digital input signal fromthe output signal of the dispersion filter.

In the other option the frequency modulated pulse is fed to severaldispersion filters on the receiver side. The differential delay timeresponse of the dispersion filters arranged on the receiver side and themodulation characteristics used on the transmitter side are herebymatched in pairs in such a way, that the spectral signal components ofthe frequency modulated pulse arrive essentially coincident at theoutput of exactly one of the dispersion filters, thus leading to anincrease in amplitude, while the output signals of the other dispersionfilters are not increased due to the differing characteristics. Thus theinput signal can be discriminated according to which dispersion filtershows an increase in amplitude.

Advantageously, surface acoustic wave filters (English: SAW- Filter:Surface Acoustic Waves) are used as dispersion filters. Hereby adispersion filter shows a frequency dependent, differential delay timeresponse that is matched to the angle modulation carried out on thetransmitter side, in such a way that the different spectral componentsof the transmitted signal arrive nearly coincident at the output of thedispersion filter in the receiver, due to their different transit timesthrough the dispersion filter, so that the output amplitude is stronglyincreased by optimum superposition of the spectral components.

The generation of the frequency modulated signal in the transmitter canbe achieved in various ways, some of which are briefly described in thefollowing.

In a preferred embodiment of the invention, at first an approximate(quasi-) Dirac pulse is generated and fed to a low-pass filter, thefilter characteristic of which shows a peak just before the criticalfrequency, and thus transforms the delta impulse to a Sinc-pulse, theshape of which is described by the Sinc-function Sinc(x)=sin(x)/x. TheSinc-shaped output signal of the low-pass filter subsequently is fed toan amplitude modulator that imprints a Sinc-shaped envelope onto thecarrier oscillation. When the signal generated in this manner is fed toa dispersive filter, a frequency modulated pulse appears at its output.Thus in this variation of the invention, on the transmitter side thedispersion filter at first expands the relatively sharp Sinc-impulseinto a frequency modulated pulse, that is wider, compared to theSinc-pulse, and possesses a correspondingly lower amplitude. On thereceiver side, a dispersion filter effects a compression of the pulsewith a corresponding increase in amplitude. Since one dispersion filtereach is used for the expansion of the pulses on the transmitter side,and the compression on the receiver side, this variation isadvantageously suited for a transceiver operation with alternatingtransmitting and receiving operation. For this, transmitter and receivercan each contain corresponding identical component modules, with onedispersion filter each, that are used for the generation of thefrequency modulated pulse in transmitting operation, and for thecompression of the received frequency modulated pulses in receivingmode.

In another variation of the invention, the generation of the frequencymodulated pulses is effected using a PLL (PLL: Phase Locked Loop) and avoltage controlled oscillator (VCO: Voltage Controlled Oscillator). Theindividual pulses of the input signal that is present in digital formare hereby at first converted to saw-tooth shaped pulses in anintegrator, whereby the direction of the rise of the individual pulsesdepends on the amplitude of the input signal. The signal generated inthis manner is then used for controlling the VCO, so that the frequencyof the output pulse linearly increases or decreases during the pulseduration, depending on the level of the input signal.

In a further variation of the invention, the generation of the frequencymodulated pulse in the transmitter is effected by a digitalsignal-processing unit, which advantageously allows the implementationof any desired modulation characteristics.

In a message transfer system according to this invention, it isnecessary to match the frequency dependent delay time response of thedispersion. filter used on the receiver side to the modulationcharacteristic of the frequency modulation carried out on thetransmitter side, so that a pulse compression in the receiver can beachieved.

In a variation of the invention, matched transmitter-receiver pairs areproduced for this purpose, so that no further tuning work is necessarywhen the system is brought into service. The previously mentioneddispersion filters preferably are executed as surface acoustic wavefilters (SAW-Filter: Surface Acoustic Waves), since such filters can beproduced with high accuracy and stability. In addition, such surfaceacoustic wave filters offer the advantage that amplitude response andphase response can be dimensioned independently of each other, whichoffers the possibility of implementing the narrow-band band-pass filterthat is required in each receiver and the dispersion filter in onecomponent. Such filters are known for other application areas, forexample from the European patent application EP 0 0223 554 A2.

In another variation of the invention, the receiver is matched to thetransmitter by varying the delay time response of the dispersion filterused on the receiver side.

Thus in one advantageous variation of the invention, the transmitter,during a matching process, emits a reference signal that preferablycorresponds to a sequence of high-levels of the input signal, wherebythe modulation characteristic of the frequency modulation carried out onthe transmitter side, or the frequency dependent delay time response ofthe dispersion filter on the receiver side, are varied, until an optimumpulse compression and increase in amplitude is achieved on the receiverside. This variation is especially advantageous when using a digitalsignal processor for filtering and processing in the receiver, sincesuch a signal processor in a simple manner allows a modification of thefrequency dependent delay time response and a correspondingoptimization, whereby the optimization process can be executedautomatically using computer control.

In a further advantageous embodiment of this variation, the datatransfer occurs block by block, whereby the matching process describedabove is carried out again for each block, to be able to dynamicallycompensate for fluctuations of the dispersion characteristics of thetransmission path.

Other advantageous, further developments of the invention areillustrated in more detail in the following figures together with thedescription of the invention's preferred embodiment. The figures show:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1 b show, as the invention's preferred embodiment, atransmitter and receiver for data transfer from an implanted medicaldevice to an extracorporeal control unit.

FIGS. 2a to 2 e show the transmitter's digital input signal, as well asseveral intermediary stages of the signal processing in the transmitterup to the transmission signal.

FIGS. 3a to 3 d show the received signal as well as several intermediarystages in the signal processing in the receiver up to the demodulatedsignal.

FIGS. 4a, 4 b show in a block diagram the transmitter and receiver ofsuch a message transfer system, with active transmission of high and lowlevels.

FIGS. 5a to 5 k show the transmitter's digital input signal in FIG. 4a,as well as several intermediary stages of the signal processing in thetransmitter.

FIGS. 6a to 6 e show the signal picked up on the receiver side, as wellas several intermediary stages of the signal processing in the receiver.

FIGS. 7 and 8 each show a modified form of the receiver illustrated inFIG. 4b with a noise suppression circuit.

DETAILED DESCRIPTION OF THE INVENTION

The transmitter illustrated in FIG. 1a is used for data transfer from animplanted medical device to an extracorporeal control unit. For example,it is possible to record an intracardial electrocardiogram (IECG) usingthe electrodes of a cardiac pacemaker, and to transmit it to aextracorporeal control unit, which displays the IECG on a monitor andsubjects it to further signal processing for diagnostic purposes. Thetransmitter shown in FIG. 1a, together with the receiver shown in FIG.1b, is well suited for this application, because the transmission canoccur with relatively low transmitting power for predeterminedrequirements on range and noise immunity, which on one hand increasesthe battery life, and on the other hand reduces the environmental impactby electromagnetic radiation, also known as Electro-smog. In addition,the transmitter has a reduced interference potential compared to othercommunications systems due to the relatively low transmitting power.

A digital input signal s₁, the time behaviour of which is shown indetail in FIG. 2a, generated for example by digitizing the IECG signal,in the transmitter is fed to a pulse shaper 2, which transforms thecomparatively wide square pulses of the input signal s₁ into shortneedle impulses, that emulate (quasi-) Dirac pulses. It can be seen fromthe illustration of the needle pulse sequence S₂ in FIG. 2b that thegeneration of the individual needle pulses is triggered by the risingedges of the square pulses of input signal s₁.

A needle pulse sequence s₂ generated in this manner is subsequently fedto a low-pass filter 3, the filter characteristic of which possesses apeak shortly before the critical frequency, so that the individualneedle pulses—as seen in FIG. 2c—are transformed to Sinc-pulses, theshape of which corresponds to the well known Sinc-functionSinc(x)=sin(x)/x.

Subsequently, the Sinc-pulse sequence s₃ is fed to an amplitudemodulator 4 (or amplitude multiplier) which modulates this signal onto acarrier oscillation of frequency f_(T), generated by oscillator 5, sothat carrier frequency pulses with a Sinc-shaped envelope are generatedat the output of the amplitude modulator, as shown in FIG. 2d. (Forrepresentative reasons the pulses are shown widened in this diagram,thus in a scale representation they are narrower.)

A dispersion filter 6 is connected after the amplitude modulator 4,which filters the modulated carrier frequency signal S₄ according to itsfrequency dependent, differential delay time characteristics. At theoutput of the dispersion filter 6 arrive—as can be seen in FIG.2e—linearly frequency modulated pulses with constant amplitude, thefrequency of which decreases during the pulse duration from a valuef_(T)+Δf/2 above the carrier frequency f_(T) to a value f_(T)−Δf/2 belowthe carrier frequency.

Thus in the transmitter shown here, the transmission of the input signals₁ is made unipolar, i.e. a transmission pulse is only generated for ahigh level of the input signal s₁, while a low level can be recognizedfrom a pause in the transmission signal s₅. For this reason transmitterand receiver can be constructed reasonably simply, each only containingone dispersion filter 6, 13.

The pulse sequence s₅ generated in this manner is subsequently fed to aband-pass filter 7, the centre frequency of which is equal to thecarrier frequency f_(T) of the frequency modulated pulses, so thatsignals outside the transmission band are filtered out.

Finally, the band-pass limited signal is supplied to antenna 9 by atransmitter amplifier 8 and emitted.

The receiver shown in FIG. 1b allows the reception of the linearlyfrequency modulated signal, emitted by the transmitter described above,as well as the demodulation and recovery of the digital input signal S₃or s₁.

For this, the signal received by the receiver's antenna 10—for examplein diversity operation—is fed to a pre-amplifier 11 and subsequently aband-pass filter 12, the centre frequency of which is equal to thecarrier frequency f_(T) of the band-pass limited transmission signal, sothat noise signals from other frequency ranges can be filtered out ofthe receiver signal. (Instead of a conventional band-pass filter asurface acoustic wave filter can be used here.) The time behaviour ofthe signal s6 prepared in this manner is shown in detail in FIG. 3a,whereby for simplification a noise free transmission path is assumed.

The received signal s6 consists of a series of linearly frequencymodulated pulses, whereby the frequency decreases during the pulseduration, according to the modulation characteristic used on thetransmitter side, from a value fT+Δf/2 above the carrier frequency fT toa value fT−Δf/2 below the carrier frequency.

Subsequently the signal s6 is fed to a dispersion filter 13, which timecompresses the individual pulses of the input signal s6, which leads toa corresponding increase in amplitude, and thus an improved signal/noiseratio.

Hereby the pulse compression utilizes the fact that the signalcomponents of higher frequency arrive at the output of the dispersionfilter 13 before the lower frequency signal components, due to thelinear frequency modulation carried out on the transmitter side. Thedispersion filter 13 compensates for the “lead” of the higher frequencysignal components by delaying these more than the lower frequency signalcomponents. Hereby the frequency dependent, differential delay timeresponse of dispersion filter 13 is matched to the modulationcharacteristic of the frequency modulation carried out on thetransmitter side, in such a manner, that the spectral signal componentsof the received signal arrive essentially coincident at the output ofdispersion filter 13. As seen in FIG. 3b, the spectral componentssuperpose to form a signal s7 with Sinc-shaped envelope for each pulse,whereby the amplitude of the individual pulses is significantlyincreased compared to the received linear frequency modulated signal s6.(It should be noted at this point that for improved clarity a distortionwas introduced in the schematic signal representations shown in thefigures. In reality the frequency-modulated pulses are closer togetherand the compressed signals are much narrower.)

Subsequently the output signal of the dispersion filter 13 is fed to ademodulator 14, which separates signal s7 from the high frequencycarrier oscillation and—as seen in FIG. 3c—generates a discrete outputsignal s8 with needle shaped pulses.

Subsequently, the original digital signal s9, the time behaviour ofwhich is shown in detail in FIG. 3d, is recovered from the needle shapedpulses using a pulse shaper 15.

FIGS. 4a and 4 b show a further message transfer system according tothis invention, which differs from the simpler embodiment example,described above and illustrated in FIGS. 1a and 1 b, most importantly bythe fact that both the high level as well as the low level of thedigital information signal are transmitted actively, which contributesto a higher noise immunity. This transmission system too is especiallysuited for data transfer from an implanted medical device to anextracorporeal control unit, due to the low demand on transmissionpower.

The transmitter shown in FIG. 4a contains a pulse shaper 17, which istriggered by a timing generator 16, using timing pulses opposite inphase, shown in FIGS. 5a, 5 b. At its output the pulse shaper emits—asshown in FIG. 5c—a sequence g1 of needle shaped pulses that form a(quasi-) Dirac delta sequence. The pulse sequence g1 generated in thismanner is subsequently fed to a low-pass filter 18, the filtercharacteristic of which possesses a peak just before the criticalfrequency, and that transforms the needle shaped pulses to Sinc-shapedpulses, which are shown in detail in FIG. 5d. Subsequently, this pulsesequence g2 is modulated onto a carrier oscillation with carrierfrequency fT, generated by the oscillator 19, using an amplitudemodulator 20. Thus, at the output of amplitude modulator 20 (oramplitude multiplier) arrives a sequence g3 of equidistant carrierfrequency pulses with Sinc-shaped envelopes. It is important in thiscontext, that the pulse sequence g3 arriving at the output of theamplitude modulator 20 is independent of the digital input signal g4,and thus does not contain any information.

Subsequently, the imprinting of the information of input signal g4 iseffected by means of an analogue switch 21, which is controlled by inputsignal g4, and, depending on the amplitude of the input signal g4,directs the pulse sequence g3, generated by amplitude modulator 20,either to a dispersion filter 22 with a frequency dependent linearlydecreasing delay time, or to a dispersion filter 23 with a frequencydependent linearly rising delay time. At their outputs, the dispersionfilters 22, 23 are connected to a further analogue switch 24 or a mixerstage, which, depending on the amplitude of input signal g4, selects theoutput signal g7, g8 of one of the two dispersion filters 22, 23 andpasses it on.

Thus at the output of the analogue switch 24 arrives—as shown in FIG.5k—a sequence g9 of carrier frequency pulses, linearly frequencymodulated pulse by pulse, whereby for a high level of the input signalg4 the individual pulses show a linearly increasing frequency during thepulse duration, whereas for a low level of input signal g4 the frequencyduring the pulse decreases linearly.

The signal arriving at the output of analogue switch 24 is subsequentlyfiltered by band-pass filter 25 to suppress interference signals locatedoutside of the transmission band. The signal obtained in this manner isthen amplified by a transmitter amplifier 26 and is emitted by thetransmitter antenna 27.

FIG. 4b shows the associated receiver that receives the signal, emittedby the transmitter shown in FIG. 4a, using an antenna 28. The receiveramplifies the signal in a pre-amplifier 29, and in a band-pass filter 30removes any interference signals, the frequency of which lies outsidethe transmission band.

Subsequently, the received signal is carried to two dispersion filters32, 33 by a switching element 31. Hereby the frequency dependent delaytime response of the two dispersion filters 32, 33 on the receiver sideis matched in pairs to the frequency dependent delay time response ofthe two dispersion filters 22, 23 on the transmitter side, in such a waythat the spectral signal components of the received signal add to apulse with increased amplitude at the output of one of the twodispersion filters, 32 or 33, while at the output of the otherdispersion filter, 33 or 32, only an attenuated pulse arrives due to themismatching.

As seen in FIGS. 6a and 6 b, the output signals g10 or g11 of dispersionfilters 32, 33 consist of a sequence of carrier frequency pulses withSinc-shaped envelopes.

The signals g10 or g11, appearing at the output of the two dispersionfilters 32, 33, are subsequently fed to a demodulator 34, 35, whichseparates the signals g10 or g11 from the carrier oscillation andgenerates needle shaped pulses, as seen in FIG. 6c or 6 d.

While each of the needle impulses at the output of demodulator 34corresponds to one high level of the input signal g4, the needleimpulses arriving at the output of the other demodulator 35 indicate lowlevels of input signal g4.

To recover the original input signal g4 from the two signals g12, g13,the two signals g12, g13 are fed to a timing generator 36 fortriggering, which generates a timing signal that reproduces the timingsignal, together with the output signals g12, g13 of the twodemodulators 34, 35 is fed to the decode 37, which recovers the originaloutput signals, g4, g14 as can be seen in FIG. 6e.

FIG. 7 shows a modified form of the receiver shown in FIG. 4b, with anoise suppression circuit 38, which can be combined with other receiversfor such Chirp signals. Due to the very close similarity of thisreceiver with the one shown in FIG. 4b, functionally equivalentcomponents are labelled by the same reference signs in the two figures.

As in the previously described receiver, the signal chirped on thetransmitter side is received through an antenna 28 and at first fed toan input amplifier 29 and a band-pass filter 30, which is tuned to thecarrier frequency and thus filters out noise signals lying outside thetransmission band. Subsequently, the signal is carried to the noisesuppression circuit 38 and split into two parallel branches, in each ofwhich two dispersion filters 39, 44 or 40, 43, inverse with respect toeach other, are connected in series. During an active transmission of alogic LOW level as well as of a logic HIGH level, one of the twodispersion filters, 39 or 40, arranged on the input side, is tuned insuch a way that a time compressed signal arrives at the output of thisdispersion filter, 39 or 40. At the output of the other dispersionfilter, 39 or 40, arrives a pulse that is time expanded to twice itsoriginal length. The two analogue switches 41, 42 interrupt the signalflow in the two branches symmetrically around the centre of thecompressed pulse, so that the time compressed pulse is suppressed andonly the time expanded pulse in the other branch remains. Hereby theanalogue switches 41, 42 are controlled through the synchronizingcircuit 46, that is triggered by the timing generator 36, and thusreproduces the timing of the output signal, and thus the transmissiontiming. The following dispersion filters 43, 44 generate the originalpulse, with original width and correspondingly also with originalamplitude, from the time expanded pulse. These pulses are then fed tothe subtracter 45, at the output of which appears essentially theoriginal pulse.

The matter is different for the noise that is caused by the noisytransmission path, and is received by the receiver together with theuseful signal. This noise is at first shifted into different directionsby the dispersion filters 39, 40. But the dispersion filter 43, 44,connected after, reverse this shift, so that the input noise isreconstructed in the two branches, except the very short portion cut outby the analogue switches 41, 42. Thus the subtraction by the subtracter45 leads to extensive suppression of the noise picked up on the receiverside.

The further processing of the signal that was prepared in this mannerthen occurs as described in the description to FIG. 4b, starting afterbifurcation 31.

The receiver shown in FIG. 8 differs from the one described above andillustrated in FIG. 7 essentially by the design and the controlling ofthe noise suppression circuit 47. Due to the extensive similarity of thetwo circuits, functionally equivalent components or component modulesare labeled by identical reference signs in FIGS. 7 and 8.

As with the receiver shown in FIG. 7, the chirped pulses are received bythe antenna 28 and at first fed to an input amplifier 29 and a band-passfilter 30, which is tuned to the carrier frequency and thus filters outnoise signals lying outside the transmission band.

Subsequently the signal is carried to the noise suppression circuit 47,which splits the signal into two parallel branches, that each containtwo dispersion filters 48, 52 and 49, 53, inverse with respect to eachother, connected in series. At the output of the noise suppressioncircuit 47 the two branches are joined by the subtracter 54, whereby thenoise in the received signal is completely suppressed by thesubtraction.

In contrast, the chirped signal is not cancelled by the subtraction inthe subtracter 54, so that the signal/noise ratio is significantlyincreased. Hereby the dispersion filters 48, 49 on the input side arematched to the chirped signals, generated on the transmitter side, insuch a way that a time compressed pulse with correspondingly increasedamplitude appears at the output of one of the dispersion filters 48, 49,whereas a time expanded pulse with correspondingly reduced amplitudeappears at the output of the other dispersion filter 49, 48. Uponarrival of the compressed pulses, the signal flow in the two branches issuppressed synchronously by the multipliers 50, 51,—as will be describedin detail—so that the compressed pulse is cut out approximately alongits envelope. The original pulse is then generated from the timeexpanded pulse by the dispersion filters 52, 53 connected after, so thatessentially the originally received signal, with a significantlyimproved signal to noise ratio, arrives at the output of the subtracter54.

The triggering of the multipliers 50, 51 occurs in fixed synchronizationwith the transmission timing rate, so that the signal in the twobranches of the noise suppression circuit 47 can be suppressed exactlyat the arrival of the time compressed pulse. For this, the receivercontains a synchronizing circuit 57, which on the input side isconnected to the timing generator 36 for synchronization. Subsequently,Sinc-pulses with amplitude 1, lying inverted with the peak towards tozero, are generated by a pulse shaper 56 and a low-pass filter 55, andare then fed to the multipliers 50, 51. The multipliers 50, 51 multiplythe signals in the two branches of the noise suppression circuit 47,either by zero or by unity, which accordingly either suppresses thesignal or leaves the signal to pass essentially unchanged. Thus themultipliers 50, 51 here have the same effect as the switching elements41, 42 in the variation of the noise suppression circuit 38 describedbefore.

The scope of the invention is not limited to the previously listedpreferred embodiments. A multitude of variations is possible that makeuse of the presented solution even in fundamentally differentimplementations. The embodiment examples shown here should only be seenas basic types of a wide spectrum of solutions.

What is claimed is:
 1. A method for wireless communication with amedical device implanted in the human body, wherein in a transmitter aninformation input signal undergoes an angle modulation and reaches areceiver through a transmission channel, and further wherein anglemodulated pulses carrying information possessing a frequency spectrumare generated in the transmitter and may be time compressed in thereceiver using a frequency dependent delay time dispersion filter, andfurther wherein the pulses are created of shorter duration and increasedamplitude compared to emitted pulses, wherein the pulses on atransmitter side undergo modulation or an encoding process and areimprinted with at least a part of information that constitutes amessage, and wherein at least a part of the information that constitutesthe message is also imprinted onto the angle modulation, wherein aquasi-Dirac pulse sequence is approximated in the transmitter and fed toa low-pass filter, the low pass filter characteristic of which possess apeak shortly before the critical frequency, and thus transforms thepulse sequence into a series of Sinc-pulses, having a shape of a Sincfunction, which subsequently is carried to an amplitude modulator, whichimprints a Sinc-shaped envelope onto each pulse of a carrieroscillation, and a signal generated after transformation is fed to adispersive filter, at an output of which arrives a frequency modulatedpulse sequence.
 2. The method of claim 1, wherein the pulses arefiltered according to a default filter response, and wherein the anglemodulation on the transmitter side and the frequency dependentdifferential delay time response of the dispersion filter on a receiverside are matched, wherein spectral signal components of angle modulatedpulses of an output signal arrive at an output of the dispersion filteressentially coincident, and with a corresponding increase in amplitude,due to a frequency dependent variable signal delay time of thedispersion filter.
 3. The method of claim 2, wherein the angle modulatedpulses are fed to at least two dispersion filters in the receiver, andfurther wherein variable delay time responses of the dispersion filtersand modulation characteristics that are used on the transmitter side arematched in pairs, wherein spectral signal components of frequencymodulated pulses arrive essentially coincident, with a correspondingincrease in amplitude, at an output of only one of the at least twodispersion filters, while this compression does not take place for thecorresponding other of the at least two dispersion filters.
 4. Themethod of claim 1, wherein the pulses undergo additional modulation, theadditional modulation selected from the group consisting of pulseposition modulation, pulse code modulation, differential pulse codemodulation, pulse delta modulation, and combinations thereof.
 5. Themethod of claim 4, wherein the angle modulation and the additionalmodulation form independent, orthogonal, or approximately orthogonalmodulation types.
 6. The method of claim 1, wherein each pulse of acarrier frequency of an input signal is subjected to the anglemodulation in the transmitter.
 7. The method of claim 1, wherein anamplitude of pulses compressed by the dispersion filter is interpretedusing a detector.
 8. The method of claim 1, the angle modulation occursaccording to a default modulation characteristic, that determines a timevariation of a phase angle during a duration of a pulse, according to apredetermined time-variant behavior, an amplitude of an angle modulatedpulse for imprinting information contained in an input signal is presetdepending on the input signal, in the receiver the angle modulatedpulses are fed to a dispersion filter, a delay time response of which ismatched to the modulation characteristic of the angle modulation by areverse time-variant behavior wherein spectral signal components of theangle modulated pulses arrive essentially coincident, and with acorresponding increase in amplitude, at an output of the dispersionfilter, an amplitude of the pulses, compressed by the dispersion filter,is evaluated, for recovery of information contained in the input signal,using a detector, the detector being an amplitude demodulator.
 9. Themethod of claim 8, wherein during pulse duration of pulse modulatedsignals, an angle, a frequency or a phase of a carrier frequency changesover time during the pulse duration, linearly or nonlinearly accordingto a predetermined profile, monotonically from a lower frequency orphase position to an upper frequency or phase position, or monotonicallyfrom an upper frequency of phase position to a lower frequency or phaseposition, wherein dispersion filters in the receiver possess acorresponding complementary response.
 10. The method of claim 9, whereinthe predetermined profile changes within a pulse sequence in relation ofindividual pulses to each other, and wherein the profile change is alsopart of information contained in the input signal.
 11. The method ofclaim 1, wherein to facilitate communication between the transmitter andreceiver, a predetermined digital reference signal is transmitted as aninput signal to align the transmitter and the receiver, duringcommunication facilitation an amplitude or a pulse duration of an outputsignal of the dispersion filter on a receiver side is measured, and amodulation characteristic used on a transmitter side, or a frequencydependent delay time response of the dispersion filter on the receiverside, is modified, until the pulse duration at an output of thedispersion filters in the receiver reaches a minimum value, or anamplitude reaches a maximum value.
 12. The method of claim 1, whereinthe signal flow in the receiver is split into two parallel branches,each with two dispersion filters with frequency dependent delay timecharacteristics, that are inverse with respect to each other, the signalflow in the two branches is connected through or interrupted for apredetermined time interval during each pulse, whereby the interruptionor connection occurs synchronous to the transmission timing rate, thetwo branches are joined on the output side by a subtracter.
 13. Themethod of claim 1, wherein the frequency of the carrier signal is in therange between 400 MHz and 1 GHz.